How do I know if I have spray foam insulation?

Open the loft hatch, use a good torch and look up at the underside of the roof slope. You can learn a lot from the hatch without climbing in. If you do go in, stay on boarded areas or the joists themselves, never step on the ceiling between joists, and don't pull or cut the foam.

Some installations include access boards and lighting: the current product approval for one open-cell roof foam requires them as part of the work^[2]. If there is no safe way in, start with the paperwork described below.

Spray foam is sprayed onto the underside of the roof, where it expands to fill the space and sets^[1]. It can cover the rafters, trusses and the underlay or sarking beneath the tiles, so the timbers themselves may not be visible^[7]. RICS says a foam-covered timber roof "cannot be fully seen or inspected"^[8].

It is not only found in lofts. The Energy Saving Trust lists empty cavity walls and the underside of suspended timber floors, where it is often applied by robot^[9].

The paperwork is the reliable way to tell; appearance only gives clues. The sources describe the two foam types, and the boards they are sometimes confused with, like this:

A common claim is that you can tell open-cell from closed-cell by pressing it with your thumb. No RICS, PCA, government or manufacturer document checked for this guide describes such a test; the government-commissioned research gives densities only^[4]. The difference between the two types is explained on what is spray foam insulation?.

It matters because, in the modelling, the type of underlay behind the foam was the main driver of moisture risk^[4]. There are three common situations. Foam often hides the layer underneath, so you may not be able to tell from the hatch^[7].

Sprayed straight onto the tiles or slates, with no underlay. The modelling rated this high risk for both foam types in every scenario, with possible wider risks to the battens, the tile fixings and the tiles themselves^[4]. RICS says most products should not be applied this way^[8]. It was not always outside the rules: a 2011 BBA approval covered spraying closed-cell foam directly onto clay tiles and slates on roofs with no underlay^[6]. The industry inspection protocol says foam on the roof covering may be assumed to be high risk^[11].

Sprayed onto bitumen felt or another felt-type underlay. The research treats felt as a high-resistance underlay, one that limits moisture escaping outwards^[4]. Over this kind of underlay with no vapour control layer, open-cell foam was high risk in both climates modelled, and closed-cell was low risk in London but high in Newcastle^[4]. RICS says not to spray onto bitumen felt^[8].

Sprayed onto a breathable membrane. This is a low-resistance underlay, modelled at a vapour resistance more than 100 times lower than felt (Sd 0.04 m against 5 m)^[4]. The current approval for one open-cell roof foam covers only this kind of underlay, and requires an air and vapour control layer (AVCL) on the room side and either counter-battens above the membrane or protection for the membrane where it dips between rafters^[2]. Over breathable underlays the modelling found low risk in London in all four cases and medium risk in Newcastle in three of four^[4].

These ratings come from computer modelling, not from inspecting real roofs, and the Building Safety Regulator says they are not installation guidance^[12]. A high-risk build-up does not mean damage has happened; it means the roof deserves a closer look. More detail is on does spray foam cause condensation or rot?.

A few things are worth writing down or photographing, because product approvals set conditions on them:

• Old insulation still on the loft floor. Leaving ceiling-level insulation in place under rafter-level foam raised the modelled mould risk^[4][12].
• Vents at the eaves covered by foam. Approvals say existing vents and ventilation gaps must be kept clear and not foamed over^[13][6].
• Cables buried in foam. One approval forbids spraying over cables that are not in conduit or trunking^[14]. Under the wiring regulations, a cable totally surrounded by thermal insulation for more than 0.5 m can carry only half its normal current^[15].
• Recessed ceiling lights. One approval allows them with a 75 mm clearance; another bans them outright^[3][16].
• Flues and water tanks. One approval says flues must not be sprayed and water tanks must be covered^[2].
• Marks on the timbers. Water marks on rafters are worth noting even where there is no foam, as in no spray foam found, but rafter after rafter carried marks consistent with condensation.

Timber that you can see is only part of the picture. RICS notes that timber can give a low moisture reading on its visible face and be wet behind the foam^[8].

The installer's homeowner pack, if you have it. The manufacturers' Code of Practice says it should record the installer, the installation date, the product type and batch, the product approval, photographs, the pre-installation survey, the condensation risk analysis and any warranty^[1]. A shorter version should be left in the loft with a contact for the full records^[1].

So look near the hatch and on the roof timbers for a label or sheet: the manufacturers' guide says roof installers often attach the installer, date, product, batch and approval details in the roof space^[17]. RICS also advises keeping the contract, calculations, photographs, moisture readings, warranties and the product approval^[8].

The product approval number (from the BBA or Kiwa) identifies the exact product and the application it was approved for^[1]. What each document proves, and what to do if it is missing, is on what paperwork you should have and spray foam product approvals explained.

When a lender, buyer or sale depends on it, when the paperwork is missing, or when someone tells you the foam must come out. RICS says spray foam may affect a surveyor's opinion of value and that the surveyor may ask for an independent specialist report^[8].

Be wary of being told you have foam, or that it must go, by someone selling removal. Trading Standards in North East Lincolnshire reported homeowners being contacted by companies claiming their foam must come out^[18]. Citizens Advice has reported removal being sold where it was not needed, and even to homes with no foam^[19]. See spray foam cold calls and scams.

An independent inspection can confirm the type, record what the foam was sprayed onto where that can be seen, and test the timber that is exposed. Foam hides the rest, and no one can assess concealed timber without exposing it.